The invention relates to a measurement transducer for measuring a current, which includes a flat conductor system having at least two conductive tracks in thermal contact with one another, and a magnetic core. The two conductive tracks pass through the magnetic core; each track passes different respective current components, which in turn give rise to opposite respective component fluxes in the magnetic core.
In my U.S. application, Ser. No. 509,447, filed on June 9, 1983, a measurement transducer of this type was proposed, in which the arrangement of a flat conductor forms a so-called reduction winding having two single conductors. Each conductor has a resistance which differs very little from that of the other conductor, and consequently different respective current components are passed through the two conductors, which, in turn, give rise to opposite respective fluxes in a magnetic core. The two single conductors each consist of a flat conductor, and are therefore in close mechanical and thermal contact with one another, so that the two single conductors maintain their resistance ratio to one another even at relatively high conductor temperatures.
In a measurement transducer of a similar type, which has become known from U.S. Pat. No. 2,831,164, issued to Johnson et al, the primary winding consists of a single flat conductor, in which there is formed a slot along a longitudinal direction thereof. Two conductive branches separated from one another by the slot extend at an angle approximately in respective opposite directions, and surround the magnetic core also in respective opposite directions. The two conductive branches or paths are not, however, in thermal contact with one another, and consequently a temperature-independent current distribution is not ensured. Large measurement errors may therefore result, particularly in the case of any high measurement currents.
From U.S. Pat. No. 4,182,982 issued to Wolf et al, there has become known a current sensing transducer, which includes a conductive current divider forming a branch path for conducting a fractional current proportional to a current to be sensed, and being applied through the divider. A compensated transformer includes a primary circuit responsive to the fractional current, and two secondary windings. An amplifier circuit controls the current input to one secondary winding in response to the output of the other secondary winding, so that the flux of the primary circuit is virtually compensated in the core, and the secondary winding current is a measure of the current to be sensed. Wolf et al do not, however, provide a folded, or U-shaped flat conductor, so that an intimate thermal contact between two current-carrying branches is not available, thus causing possible inaccuracies in the current measurement, particularly of large currents.
From Swiss patent No. 537,085, issued to Hentschel et al, there has become known a current transducer for obtaining a voltage proportional to a current to be measured. Like the aforementioned Wolf et al patent, the Hentschel et al patent does not provide a folded, or U-shaped flat conductor, which would permit intimate thermal contact between two current-carrying branches, and the construction disclosed in that reference is therefore subject to inaccuracies similar to those arising in the Wolf et al reference, particularly in the case of large currents.